1. Field of the Invention
The present invention is directed to a method for automatically optimizing AV delay adjusted in an implantable cardiac stimulation device by using and analyzing parameters derived from heart sound.
2. Background
Implantable medical devices such as cardiac pacemakers and cardioverter defibrillators are configured to monitor the electrical activity in various chambers of a patient's heart. In doing so, the devices can adjust selected operational parameters to maintain desired cardiac function. One such cardiac function is cardiac output and one such operational parameter is atrioventricular delay (hereinafter “AV delay”). The proper setting of the AV delay can be crucial in establishing and maintaining the desired cardiac function, which contributes markedly to the patient's quality of life. It is recognized that improper setting of such device parameters, not only has a negative effect on the patient's quality of life, but may create permanent functional impairment of the patient's heart over time. Moreover, manual optimization of operational parameters such as AV delay, which may be undertaken at implant or at follow-up, may not prove to be optimum at some later date due to changes in the patient's health status, activity level, medication intake, disease progression as well as other factors impacting cardiac function.
The aim of pacing therapies in heart failure patients is the optimization of cardiac function. Implantable pacemakers are increasingly used in patients with congestive heart failure because they have proven to be very effective in enhancing cardiac function. Mechanisms that contribute to such functional improvement include an increase in filling time, improved cardiac contractility, improved right ventricular and left ventricular systolic and diastolic function, greater cardiac output and a decrease in mitrial regurgitation. However, unless stimulation devices are optimized for each individual patient, it is unlikely that appropriate and efficient pumping action and therefore cardiac output will be achieved. In that regard, it is recognized that adjusting the AV delay will either directly or indirectly affect one or more of the above identified mechanisms. Accordingly, optimization of the AV delay achieved automatically by continuous measurement and monitoring of several parameters, in particular those related to heart sound, can further improve cardiac function. Heretofore, abnormal heart sounds have been detected by the use of an acoustic sensor located in proximity to a patient's heart as is described in U.S. Pat. No. 5,554,177 to Kieval et al. The characteristics of the heart sounds, detected by the acoustic sensor, are detected during adjustments in the timing sequence of pacing pulses and pacing therapy is adjusted to achieve an improved heart function. The method described requires the use of a separate acoustic sensor(s) or microphones which not only compounds the complexity of the system, but markedly adds to its cost. Moreover the sensors as described in the '177 patent, are located outside of the stimulation device and placed at various locations in the body such as the chest and sternum. Obviously, this requires significant additional surgery to implement the system with the attendant major increase in patient discomfort as well as the cost of implant. Accordingly what is needed is a reliable and minimum cost approach to implementing heart sound detection and processing to optimize AV delay settings for improving cardiac function, preferably utilizing an activity sensor typically included in rate responsive cardiac stimulation devices.